Device for calibrating a transmissometer

ABSTRACT

A device for resetting the zero calibration of an opacity sensing meter (transmissometer) made up of a light source, which may be located on one side of a smoke stack, and a sensing element located on the other side of a smoke stack. The rezeroing device will re-zero the sensing element without using the light passing through the stack. The device samples the light at the source side of the stack and then generates an output from an auxiliary source located on the sensor side of the stack such that excitation of the normal system sensor by the auxiliary source is the same as excitation would be to the sensor by the normal source.

United States Patent [191 Brugger [451 Nov. 26, 1974 DEVICE For: CALIBRATING A TRANSMISSOMETER [76] Inventor: Richard D. Brugger, 4818 Walker Blvd, Erie, Pa. 16509 [22] Filed: Oct. 26, 1972 [21] Appl. No.: 300,915

[52] US. Cl 356/207, 356/201, 356/243 [51] Int. Cl. G0ln 21/12, 00111 21/26 [58] Field of Search 356/73, I03, 207, 201

[56] References Cited UNITED STATES PATENTS 2,877,453 3/1959 Mendenhall, Jr. 356/103 3,376,425 4/1968 Kraus et al 356/73 3,453,049 7/1969 Wager, Jr. 356/73 OTHER PUBLICATIONS Optical Properties and Visual Effects of Smoke Stack Plumes, Public Health Service, HEW, 1967.

Primary Examiner-Vincent P. McGraw [5 7] ABSTRACT A device for resetting the zero calibration of an opacity sensing meter (transmissometer) made up of a light source, which may be located on one side of a smoke stack, and a sensing element located on the other side of a smoke stack. The re-zeroing device will re-zero the sensing element without using the light passing through the stack. The device samples the light at the source side of the stack and then generates an output from an auxiliary source located on the sensor side of the stack such that excitation of the normal system sensor by the auxiliary source is the same as excitation would be to the sensor by the normal source.

6 Claims, 2 Drawing Figures PATENTEL NGV 2 6 I974 suzgrior 2 DEVICE FOR CALIBRATING A TRANSMISSOMETEIR GENERAL DESCRIPTION OF THE INVENTION Increased interest in the control of atmospheric pollution puts requirements on the monitoring of effluence from smoke stacks. One such characteristic to be monitored is the opacity or optical density of the flue gas which is measured on a scale of neutral density, per cent opacity, or by the Ringelmann Scale. Such systems are known as transmissometers. Transmissometers have a light source on one side of the stack and a sensing means on the other. The zero calibration point of the meter of the sensing means is normally set with the light on and no smoke in the stack. In practice, it is seldom that the operator has a stack with clear gas in it to work with.

After the zero point of the transmissometer is originally set, there are factors which dictate that the meter should be re-zeroed:

1. Aging of lamps with the resulting light output;

2. Lamp replacement (each lamp does not have the same initial lumen output);

3. Accumulation of dirt on the lenses and windows facing the stack, with subsequent reduction in the amount of light transmitted;

4. Change in the opacity meters electronics (drift) over a period of time.

Such factors are taken into account by the embodiment of FIG. 1, which is a means to compensate for the above system changes, with the stack in operation.

The embodiment of FIG. 2 provides means to compensate for all of the above system changes and, in addition, provides means to compensate for accumulation of dirt on the window in front of the sensor used in the normal operation of the monitoring system.

The means to zero calibrate the system without going through the stack, as well as to check the zero point of the opacity meter, is also needed because in operating systems with certain fuels, it is not possible to get a clear gas in the stack for calibration purposes unless the entire boiler or smoke producing system is out for some other reason.

The device disclosed herein is suitable for use with a transmissometer, such as disclosed in Pat. No. 3,376,425 to Howard Kraus.

OBJECTS OF THE INVENTION It is an object of the invention to provide a means to externally zero a transmissometer.

Another object of the invention is to provide a means to sample light at the source of a stack and then generate an output signal from an auxiliary source located on the sensor side of the stack, such that excitation of the normal system sensor by the auxiliary sensor is the same as excitation would be provided to the normal sensor system by the normal sensor source acting alone, if the stack were clear. The auxiliary source is then used as the input to the normal system sensor for the purpose of establishing the meters zero calibration point by external means. Furthermore, the system constants are stored in passive elements, (for example, resistors), as will be described.

Another object is to provide a re-zeroing system for an opacity meter wherein resistors are used as memory elements to store the effects of system constants.

GENERAL DESCRIPTION OF THE DRAWINGS FIG. 1 shows one embodiment of a stack monitoring apparatus with its circuit diagram.

FIG. 2 shows another embodiment of a stack monitoring apparatus with circuit diagram.

DETAILED DESCRIPTION OF THE DRAWINGS The system illustrated in FIG. 1 comprises a stack 20, a normal system source 1 for example, a light bulb, a normal system sensor 11 for example, a photovoltaic photocell, a power supply 30, an opacity meter 3, and an auxiliary source 2, a Variac 4, or other suitable means to adjust the voltage on light source 2, an auxiliary sensor 12, a gang selector switch 40, two feedback resistors 15 and 15', a dynamic calibration meter 16, and an operational amplifier 14.

The source of voltage 120 volts is connected through switch SW-l to the circuit. The switch SW-2 turns on the normal source 1 and SW-3 connects the voltage to the Variac 4 and thence turns on the source 2.

Septums 21 and 22 are glass prisms which deflect light approximately from the adjacent light source, that is, a part of the light from normal system source 1 is deflected by septum 21 on to auxiliary sensor photovoltage cell 12 and a part of the light from auxiliary source 2 is deflected by septum 22 onto the normal system sensor 11.

The performance of an operational amplifier (OP- .AMP.) is substantially determined by the external components. Various configurations of these external components are possible. The configurations used here as the positive (non-inverting) input, grounding, and feedback resistors 15 and 15 from the output terminal to the negative (inverting) input. The photovoltaic photocell in various situations is connected into the negative input, which appears as a very low impedance compared to photovoltaic cells internal impedance, consequently it delivers essentially its short-circuit current in the operational amplifier. Short-circuit current is a linear function of illumination for this type of photocell. Consequently, current into the operational amplifier is essentially a linear function of illumination. The magnitude of the operational amplifier 14 output voltage is the cell current times the resistance of the feedback resistor. Thus we can define the gain of the operational amplifier in this configuration'as the magnitude of the feedback resistors (15 and 15 in FIG. 1). Gain in this sense is taken as the slope of the transfer function where current is the input and voltage is the output.

In a practical sense, operational amplifier will deviate from mathematically perfect models and may alter performance somewhat over periods of time. Therefore, it is advantageous to use the same operational amplifier for both cell measurements and thereby washout any cumulative errors. Any changes in internal operational amplifier performance from initial setup, with clear stack, and the external zero operations that follow, and between subsequent external zero operations, is of no consequence.

Further discussions of this type of circuit appear in the literature, such as:

Operational Amplifiers, Design and Application by Tobey, Graeme and Huelsman, pages 232 and 233. The inventors own personal activity on OP. AMPS., entitled Extending an Operational Amplifier Bandwidth to 50 MHZ by Richard D. Brugger in ELECTRONIC DESIGN magazine, May 25, 1964.

GENERAL SYSTEM OPERATION The system is operated by sampling the light at side of the stack 20 from the normal source 1 with gang selector switch 40 in position a. Switch 40 is a gang switch having six banks of fixed contacts and six movable contacts A, B, C, D, E and F which are moved in unison by common mechanical connector 41.

The function of switch 40 is to select either the photocell 11 or the associated resistor or the photocell 12 or resistor 15'. Switch 40 also switches meter 3 in and out of the system.

An output is generated from the auxiliary source 2 such that excitation into the normal system sensor 11 in FIG. 1 by the auxiliary source 2 acting alone is the same excitation that would be provided the normal system sensor 1 1 by the normal system source 1 still acting alone if the stack were clear. With gang selector switch 40 in position a, the auxiliary source 2 is then used as the input to the normal system sensor 11 for the purpose of establishing the opacity meters zero calibration point by external means. This is done through a channel independent of the stack. The system constants are stored in two passive elements, resistors 15 and 15'.

PRELIMINARY ADJUSTMENT OF AUXILIARY LIGHT SOURCE INTENSITY Before the system constants can be stored, the intensity of source 2 is adjusted to give the same opacity meter reading as source 1. This step in effect moves source 1 with any dirt on the window 18 in front of it, across the stack into the position of source 2. However, any dirt on window 19 is not compensated for by the apparatus in this first embodiment. The operator first observes the scale of the opacity meter 3 with the normal system source 1 turned on and gang selector switch 40 in position a. The operator may then adjust the zero control 31 of the opacity meter 3 to give him a convenient reading, for example, 20%. The operator then turns the normal source 1 off and turns on the auxiliary source 2. The auxiliary source 2 has an adjusting means by way of Variac 4 whereby it can be adjusted by the operator. The operator adjusts the auxiliary source 2 by means of a Variac 4 or other suitable means, so that the opacity meter 3 is returned to the convenient reading selected.

ESTABLISHING SYSTEM CONSTANTS The operator is then ready to set the system constants, resistors 15 and 15 Auxiliary source 2 is turned on, the normal system sensor 11 is connected to operation amplifier 14 with feedback resistor 15 by placing gang selector switch 40 in position b. The output of operation amplifier 14 is fed into meter 16, called the dynamic calibration meter. The operator adjusts resistor 15 to give a specific reading on the meter. The choice of the reading is somewhat arbitrary but, for example, could be half scale or 50.

The operator then turns off source 2 and turns on source 1 and switches the auxiliary sensor photo voltage cell 12 into the amplifier 14 with feedback resistor 15' by placing gang selector switch 40 in position 0. The operator now sets resistor 15 to give the 50 reading on the dynamic calibration meter l6.

The system constants have thus been established as the settings of resistors 15 and 15. Once 15 and 15 are established, they are not changed, but constitute the system memory.

The sensors 11 and 12 are photovoltaic cells, and should properly have spectral filtering in front of them and should be maintained at a constant temperature. Other cells could be used if properly connected. Perfonnance of the operation amplifier follows the classical analysis of a high gain amplifier with feedback.

THE EXTERNAL ZERO SYSTEM (EMBODIMENT OF FIG. 1)

Once 15 and 15 are set, as described above, it is possible to external zero the system at any time even with a smoke reading of five Ringelmanns (l00% opacity). The effect of the external zero procedure is to move the source 1 with any dirt on the window 18 in front of it across stack 20 into the position of source 2. This embodiment, however, does not compensate for any dirt on window 19. External zero is a routine maintenance procedure that can be performed daily or whenever desired.

The operator has source 1 on, he connects photocell 12 to dynamic calibration meter 16 through resistor 15 and operation amplifier 14 by placing gang selector switch 40 in position b. He reads the dynamic calibration meter 16, and proceeds to connect photocell 11 to dynamic calibration meter 16 through resistor 15 and operation amplifier 14 by placing gang selector switch 40 in position 0. The operator then turns off source 1 and turns on source 2 and adjusts the intensity of source 2 by means of Variac 4 or other suitable means until a dynamic calibration meter 16 reads the value previously obtained. The operator then switches on normal system sensor 11, to the opacity meter 3 by placing gang selector switch 40 in position c and adjusts the zero control 31 to zero the meter 3. The external zero is now complete, and the operator turns off source 2 and turns on source 1, and the system is read ing smoke opacity.

THE EMBODIMENT OF FIG. 2

Now with reference to the embodiment of FIG. 2, the invention disclosed provides another means to externally zero a transmissometer or opacity meter 103.

The system illustrated in FIG. 2 comprises a stack 120, a normal system source 101, for example, a light bulb, a normal system sensor 110, for example, a photovoltaic photocell, a photosensor 113, a power supply 130, a transmissometer 103 (or opacity meter), and an auxiliary source 102, a Variac 104 (or other suitable means of source adjustment), an auxiliary sensor 112, a gang selector switch 140, two feedback resistors and 115', a dynamic calibration meter 116, and an operational amplifier 114.

The sensors 110, 112 and 113 are photovoltaic cells, and should properly have spectral filtering in front of them and should be maintained at a constant temperature. Other cells could be used if properly connected. Performance of the operation amplifier follows the classical analysis of a high gain amplifier with feedback. Once 11S and 115 are established, they are not changed, but constitute the system memory.

GENERAL OPERATION OF THE EMBODIMENT OF FIG. 2

The system is operated by sampling light at the side of the stack 120 at the normal source 101 with gang selector switch 140 in position a. The source of voltage 120 volts is connected through switch SW-l to the circuit. The switch SW-2' turns on the normal source 101 and SW-3 connects the voltage to the Variac 104 and thence turns on the source 102.

Septums 121 and 122 are glass prisms which deflect v light approximately 90 from the adjacent light source,

that is, a part of the light from normal system source 101 is deflected by septum 121 on to auxiliary sensor photovoltage cell 1 12 and a part of the light from auxiliary source 102 is deflected by septum 122 onto the normal system sensor 11 1. Switch 140 is a type of switch such as switch 40 of FIG. 1. The function of switch 140 is to select either the photocell 112 and the resistor 115' or the photocell 113 and resistor 115.

An output is generated from the auxiliary source 102 such that excitation from the normal system sensor 1 by the auxiliary source 102 acting alone is the same excitation that would be provided the normal system sensor 110 by the normal system source 101 acting alone if the stack were clear. The auxiliary source 102 is then used as the input to the normal system sensor 110 for the purpose of establishing the opacity meters zero calibration point by external means. This is done through a channel independent of the stack. The system constants are stored in two passive elements, resistors 115 and 115'.

PRELIMINARY ADJUSTMENTS OF AUXILIARY v LIGHT SOURCES OF EMBODIMENT FIG. 2

Before the system constants can be stored, the intensity of source 102 is adjusted to give the same' opacity meter reading as source 101. This step in effect moves The operator then turns off, source 102 and turns on source 101 and switches the auxiliary sensor photo voltage cell 112 into the dynamic calibration meter through amplifier 114 and feedback resistor 115 by placing gang selector switch 140 on position c. The operator now sets resistor 115 to give the 50 reading on the dynamic calibration meter 116, The system constants have thus been established as the settings of resistors 115 and 115'. Once the settings of resistors 115 and 115 have been established, they are not changed but constitute the system memory.

. THE EXTERNAL ZERO SYSTEM (EMBODIMENT OF FIG. 2)

Once 115 and 115 are set, as described above, it is possible to extemalzero the system at any time even with a smoke reading of five Ringelmanns 100% opacity). The effect of the external zero procedure is to I be performed daily or whenever desired.

source 101 with any dirt on the window 118 in front of it across stack 120 into the position of source 102. The operator first observes the scale of the opacity meters with the normal system source 101 turned on. The operator may then adjust the zero control 131 of the opacity meter 103 to give him a convenient reading, for example The operator then turns the normal source 101 off and turns on the auxiliary source 102. The auxiliary source 102 has an adjusting means by way of variac 104 whereby it can be adjusted by the operator. The operator adjusts the auxiliary source 102 by means of variac 102, or other suitable means, so that the opacity meter 103 is returned to the convenient reading selected.

ESTABLISHING SYSTEM CONSTANTS OF EMBODIMENT OF FIG. 2

The operator is then ready to set the system constants, resistors 115 and 115'. Auxiliary source 102 is turned on, the photocell 113 is connected to the dynamic calibration meter 116 through operation amplifier 114 and feedback resistor 115 by placing gang selector switch 140 in position b. The output of operation amplifier 114 is fed into dynamic calibration meter 116. Theoperator adjusts resistor 115 to give a specific reading on the meter. The choice of the reading is somewhat arbitrary but, for example, could be half scale or 50.

The operator'has source 101 on, he connects photocell 112 to the dynamic calibration meter 116 through resistor 115 and operation amplifier 114 by placing gang selector switch 140 in position b and reads the dynamic calibration meter 116. He proceeds to connect photocell 113 to dynamic calibration meter 116 through resistor 115' and operation amplifier 114 by placing gang selector switch 140 to position c. The operator then turns off source 101 andturns on source 102 and adjusts the intensity of source 102 by means of Variac 104 or other suitable means until a dynamic calibration meter 116 reads the value previously obtained. The operator then switches onnormal system sensor 110 by placing gang selector switch 140 in position a and adjusts the iero control 131 to zero the opacity meter 103. The external zero is now complete,

and the operator turns off source 102 and turns on source 101, and the system is reading smoke opacity.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of calibrating an opacity meter having a first light source and a second light source, a first sensor and a second sensor, a calibration meter, an operational amplifier,

supporting said first light source and said first sensor on a first side of an opaque medium,

and supporting said second light source and said sec-- c. adjusting said constants by adjusting said first constant means to give a second selected reading on said calibration meter with light from said first light source impinging on said second sensor;

d. and setting said second constant means to give said second selected reading.

2. The method recited in claim 1 wherein said second constant means is set with light from said second light source impinging on said first sensing means and said first sensing means being connected to said calibration meter through said second constant means and said operation amplifier, adjusting said second constant means to give said second selected reading on said-calibration meter, whereby the system constants are set for all subsequent use.

3. Rezeroing an opacity meter having its constants set according to the method recited in claim 1 by a. impinging said first light source on said second sensing means to give a first reading on said calibration meter,

b. impinging said second light source on said first sensing means and adjusting the intensity of said second light source to give said second reading on said calibration meter, equal to said first reading.

4. An apparatus for recalibrating a transmissometer made up of a first light source disposed on a first side of a stack,

and a first sensing means disposed on a second side of a stack,

said recalibrating means comprising a second sensing means disposed on said first side of said stack, and a second light source disposed on said second side of said stack,

a dynamic calibration meter connected to said system,

an operation amplifier,

and a first system constant and a second system constant comprising resistors,

means to connect said first sensing means to said dynamic calibration meter,

means to connect said second sensing means to said dynamic calibration meter,

means to adjust the intensity of said second light source to an intensity effectively equal to the light from said first light source,

means to adjust said first system constant and to adjust said second system constant whereby the output from said first sensing means to said dynamic calibration meter is equal to the output of said second sensing means to said dynamic calibration meter.

5. The apparatus recited in claim 4 wherein said first sensing means comprises two sensing elements, one sensing element being connected to said opacity meter, the other being selectively connected to said dynamic calibration meter. l

6. The apparatus recited in claim 4 wherein said first sensing means comprises one sensing element, said sensing element having means to connect to said opacity meter and to said dynamic calibration meter. 

1. A method of calibrating an opacity meter having a first light source and a second light source, a first sensor and a second sensor, a calibration meter, an operational amplifier, supporting said first light source and said first sensor on a first side of an opaque medium, and supporting said second light source and said second sensor on a second side of said opaque medium, connecting a first constant means and a second constant means to said opacity meter, setting the intensity of said second light source by a. connecting the light from said first light source impinging on said first sensor, adjusting said opacity meter to a first selected reading; b. adjusting the intensity of said second light source to give said first selected reading on said opacity meter with light from said second light source impinging on said first sensor; c. adjusting said constants by adjusting said first constant means to give a second selected reading on said calibration meter with light from said first light source impinging on said second sensor; d. and setting said second constant means to give said second selected reading.
 2. The method recited in claim 1 wherein said second constant means is set with light from said second light source impinging on said first sensing means and said first sensing means being connected to said calibration meter through said second constant means and said operation amplifier, adjusting said second constant means to give said second selected reading on said calibration meter, whereby the system constants are set for all subsequent use.
 3. Rezeroing an opacity meter having its constants set according to the method recited in claim 1 by a. impinging said first light source on said second sensing means to give a first reading on said calibration meter, b. impinging said second light source on said first sensing means and adjusting the intensity of said second light source to give said second reading on said calibration meter, equal to said first reading.
 4. An apparatus for recalibrating a transmissometer made up of a first light source disposed on a first side of a stack, and a first sensing means disposed on a second side of a stack, said recalibrating means comprising a second sensing means disposed on said first side of said stack, and a second light source disposed on said second side of said stack, a dynamic calibration meter connected to said system, an operation amplifier, and a first system constant and a second system constant comprising resistors, means to connect said first sensing means to said dynamic calibration meter, means to connect said second sensing means to said dynamic calibration meter, means to adjust the intensity of said second light source to an intensity effectively equal to the light from said first light source, means to adjust said first system constant and to adjust said second system constant whereby the output from said first sensing means to said dynamic calibration meter is equal to the output of said second sensing means to said dynamic calibration meter.
 5. The apparatus recited in claim 4 wherein said first sensing means comprises two sensing elements, one sensing element being connected to said opacity meter, the other being selectively connected to said dynamic calibration meter.
 6. The apparatus recited in claim 4 wherein said first sensing means comprises one sensing element, said sensing element having means to connect to said opacity meter and to said dynamic calibration meter. 